We all know that somewhere in this unimaginably vast universe of ours, there exists at least one planet that harbors life, or did at one time.
However, unqualified scientific proof of the existence of extraterrestrial life has been lacking. This past week, we got another tantalizing clue courtesy of the Perseverance Rover, which has been exploring the Jezero Crater on Mars. "This is an area in the planet's northern hemisphere that once was flooded with water and home to an ancient lake basin," according to Reuters.
Perseverance is the first interplanetary robot tasked specifically with finding signs of life on another planet. A paper published on Wednesday offers evidence of possible past microbial life on the Red Planet that Acting NASA Administrator Sean Duffy says "is the closest we have ever come to discovering life on Mars."
A potential "biosignature" of life was found in the sediment formed by the ancient lake bed. It contains two intriguing minerals: vivianite, an iron phosphate mineral; and greigite, an iron sulfide mineral.
Both minerals can be formed as a waste product of microbes in the mud.
What Perseverance found "was a rock streaked in a range of colors—red, green, purple, and blue—flecked with poppy-seed-like dots and decorated with what the Perseverance scientists compared to dull yellow leopard spots," as colorfully described by Time magazine.
"These reactions appear to have taken place shortly after the mud was deposited on the lake bottom. On Earth, reactions like these, which combine organic matter and chemical compounds in mud to form new minerals like vivianite and greigite, are often driven by the activity of microbes," Stony Brook University planetary scientist Joel Hurowitz said. Hurwitz led the study that was published in Nature.
The evidence is compelling but hardly cinches the case for past life on Mars.
"I want to remind everyone that what we're describing here is a potential biosignature that is a characteristic element, molecule, substance or feature that might have a biological origin but requires more data or further study before reaching a conclusion about the presence or absence of life," Senior Scientist for Mars Exploration in the Planetary Science Division at NASA Headquarters Lindsay Hayes said.
Either way, the findings do demonstrate that notably complex reactions once occurred on Mars — organic or not — adding yet more layers to the planet humans have been trying to decode since the dawn of astronomy.
To get into some specifics, the samples Perseverance collected that appear to harbor those exciting minerals were found in what's known as the "Bright Angel" formation within the northern margin of Neretva Vallis. Within that formation, one particular rock is of great interest to researchers. It's named "Cheyava Falls."
Not too long ago, when Cheyava Falls was first presented to the public, it made headlines around the world because scientists were openly fawning over the specimen's peculiar, dotty features that resembled "poppy seeds" and "leopard spots." The latter, which are millimeter-size blobs, are each surrounded by black rings that scientists determined contain iron and phosphate after studying them with Perseverance's toolkit. Both substances can result from chemical processes on Earth that are driven by microbes.
"What we saw in this rock were these layers of very fine-grained, rusty red mud stone that had in them these incredible features," Hurowitz said. "These textural features told us that something really interesting had happened in these rocks, some set of chemical reactions occurred at the time they were being deposited."
Ever since the 1976 Viking landers discovered what was believed to have been organic reactions in soil samples, later to be dismissed as a natural process, scientists have been of two minds about Mars biology. Is what they're seeing geological or biological?
That Viking sample that showed positive for microbes in Martian soil is being reexamined in light of other, more recent discoveries. There has even been speculation that the Viking collection process actually killed some living microbes, which is why the test was so ambiguous.
This debate over life on Mars, past or present, will never be resolved by robots. We're going to have to go there, walk around, examine the most likely places for life to have arisen, and use our human intuition and sixth sense to solve the riddle.
